To meet the ever growing requirement for smaller dimensions of electronic components, electronic devices are known from the prior art that are in the form of packages in which the components are placed, for example ceramic packages or plastic packages, the latter category being the most widespread. The package comprises a support made of insulating material on which the components are arranged, on one or more levels, the components being covered with an encapsulant, for example made of plastic of the epoxy type. On each of its internal and external faces, the support has connection pads, respectively for connection of the components and for connection of the package to a substrate.
FIGS. 1A and 1B show, respectively, examples of a BGA (Ball Grid Array) package 1 and an example of an LGA (Land Grid Array) package 1′ that are intended to be connected to a substrate 100. Only the outline 10 of the package has been shown. Placed inside are the support and the electronic components on one or more levels (not shown). The packages are equipped with external connection pads 11 for connection to connection pads 101 on the substrate 100. In the example shown in FIG. 1A, which is the most common, the external connection pads 11 of the package are provided with balls 12, hence the name BGA, making it very easy to position the facing connection pads. The balls are soldered to the pads 101 on the substrate by providing a layer 102 of solder, for example, a tin/lead alloy or a lead-free alloy. However, ball-less soldering, directly between pads, is also possible. This is the example of LGA packages, as shown in FIG. 1B. In this case, provision of a solder layer 103 allows the external connection pad 11 from the package to be soldered directly to the connection pad 101 on the substrate.
The fabrication of packages as described in the FIG. 1A or 1B, for example requires a heating step to bond the connection pads on the package to the connection pads on the substrate by soldering them together, whether or not they are equipped with balls. During this step, the package passes through a high-temperature oven. The temperature may reach about 230° C. or even higher when a lead-free solder is employed. Owing to the size of this type of package (typically measuring from 5 to 50 mm), the number of connection pads is considerable (several hundred or even several thousand) and, when passing through the oven, the temperature reached at the pads located in a central position of the package is much lower (by 40° C. to 80° C.) than that reached at the pads located on the periphery, in particular in plastic packages owing to the low thermal conduction of the materials used. This temperature nonuniformity at the various connection pads means that the heating temperature of the oven must be increased further so as to ensure that the temperature reached at the center will be sufficient for soldering, with the risk of damaging the electronic components in the package, and also all those outside the package.